A novel amperometric immunosensor has been developed for the detection of salivary secretory immunoglobulin A（sIgA）based on layer-by-layer（LBL）assembly of gold nanoparticles-thionine（GNPs-THI）on the Nafion modified glassy carbon electrode（GCE）and the sIgA was adsorbed by the formative monolayer GNPs

nonspecific adsorption sites were blocked by horseradish peroxidase（HRP）eventually.This immunosensor has high sensitivity

good specificity

convenient to detect sIgA with a detection limit of 3.0mg·L-1

the linear range is from 6.5 to 300mg·L-1

the response time achieved 95%

steady state time was less than 20s.Some factors which influence on the biosensor were investigated

such as the concentration of antibody and substrate

pH and temperature

incubation time

interferents.To detect salivary samples

the method of biosensor and ELISA are parallel used.The results indicate that the two methods had significant correlation（R=0.98932

P<0.001）

so it can be used to swiftly and accurately detect salivary sIgA and to judge the localimmunity of human body.